A guide to commonly used plastics (20 types)

A guide to commonly used plastics (20 types)

Plastic is a macromolecular compound (macromolecules) polymerized by polyaddition or polycondensation reaction with a monomer as a raw material, consisting of synthetic resin and fillers, plasticizers, stabilizers, lubricants, dyes and other additives.

A guide to commonly used plastics (20 types)

The main component of plastic is resin. Resin refers to a polymer compound not mixed with various additives. The term resin was originally named after lipids secreted by animals and plants, such as rosin and shellac. Resin makes up 40% to 100% of total weight of plastic. The basic properties of plastics are mainly determined by nature of resin, but additives also play an important role. Some plastics are mainly composed of synthetic resins without additives or with a small amount of additives such as plexiglass, polystyrene, etc.

A guide to commonly used plastics (20 types)

1.ABS copolymer of acrylonitrile, butadiene and styrene

Typical application:

Automobiles (dashboards, tool hatches, wheel covers, mirror boxes, etc.), refrigerators, high-intensity tools (hairdryers, blenders, food processors, lawn mowers, etc.), phone cases, keyboards typewriters, recreational vehicles such as golf carts and jet skis.

Injection molding process conditions:

Drying: ABS material is hygroscopic and needs to be dried before processing. The recommended drying mode is at least 2 hours at a temperature of 80-90°C. The temperature of material must be guaranteed to be below 0.1%.

Melting point: 210~280℃, recommended temperature: 245℃.

Mold temperature: 25~70℃. (The temperature of mold will affect finish of plastic parts, lower temperature will cause finish to deteriorate).

Injection pressure: 500~1000 bar.

Injection speed: medium to high.

Chemical and physical properties:

ABS is synthesized from three chemical monomers: acrylonitrile, butadiene and styrene. Each monomer has different characteristics: acrylonitrile has high strength, thermal stability and chemical stability; butadiene has impact strength and impact resistance; Styrene is characterized by easy processing, high finish and high strength. From a morphological point of view, ABS is a non-crystalline material. Polymerization of three monomers gives a terpolymer with two phases, a continuous styrene-acrylonitrile phase and a dispersed polybutadiene rubber phase. The properties of ABS mainly depend on ratio of three monomers and molecular structure in two phases. This allows for greater flexibility in product design and thus produces hundreds of different qualities of ABS materials on market. These different material qualities provide different properties such as medium to high impact resistance, low to high finish, high temperature deformation characteristics and others. ABS material has very easy workability, appearance, low creep and excellent dimensional stability, as well as high toughness.

2.PA6 polyamide 6 or nylon 6

Typical application:

It is widely used in structural parts due to its good mechanical strength and rigidity. Due to its good wear resistance properties, it is also used in production of bearings.

Injection molding process conditions:

Drying: Since PA6 easily absorbs water, special attention should be paid to drying before processing. If material is supplied in waterproof packaging, container must be tightly closed. If humidity is more than 0.2%, it is recommended to dry with hot air at a temperature above 80°C for 16 hours. If material was onair for more than 8 hours, vacuum drying at 105°C for more than 8 hours is recommended.

Melting point: 230~280°C, 250~280°C for improved varieties.

Mold temperature: 80~90℃. Mold temperature significantly affects crystallinity, which in turn affects mechanical properties of plastic parts. Crystallinity is important for structural parts, so a mold temperature of 80-90°C is recommended. For thin-walled plastic parts with long process times, a higher mold temperature is also recommended. Increasing mold temperature can increase strength and rigidity of plastic part, but decrease toughness. If wall thickness is more than 3mm, it is recommended to use a low temperature mold at 20~40°C. For materials reinforced with fiberglass, temperature of mold must be above 80°C.

Injection pressure: typically 750 to 1250 bar (depending on product material and design).

Injection speed: high speed (slightly lower for reinforced materials).

Rosette and gate: Since curing time of PA6 is very short, position of gate is very important. The gate opening must not be less than 0.5*t (where t is thickness of plastic part). When using a hot runner, gate size should be smaller than when using a conventional groove, as hot runner can help prevent premature solidification of material. If a submersible valve is used, minimum valve diameter must be 0.75 mm.

Chemical and physical properties:

In terms of chemical and physical properties, PA6 is very similar to PA66, but has a lower melting point and a wide operating temperature range. Its impact and solvent resistance is better than PA66, but it is also more hygroscopic. Since many of quality characteristics of plastic parts depend on hygroscopicity, this should be fully taken into account when developing products using PA6. Various modifiers are often added to improve mechanical properties of PA6. Glass is most common additive, and sometimes synthetic rubber such as EPDM and SBR is added to improve impact resistance. For products without additives, shrinkage rate of PA6 is between 1% and 1.5%. The addition of glass fiber additives reduces shrinkage to 0.3% (but slightly higher towards process). The shrinkage of molded assemblies is mainly affected by crystallinity and hygroscopicity of material. The actual shrinkage rate also depends on design of plastic part, wall thickness, and other process parameters.

3.PA12 polyamide 12 or nylon 12

Typical application:

Water meters and other commercial equipment, cable glands, mechanical cams, sliding mechanisms and bearings.

Injection molding process conditionseat:

Drying: Moisture must be kept below 0.1% before processing. If material is stored outdoors, it is recommended to dry it with hot air at 85°C for 4-5 hours. If material is stored in an airtight container, it can be used immediately after 3 hours of temperature equalization.

Melting point: 240~300°C; for materials with normal characteristics, it should not exceed 310°C, and for materials with fire-resistant characteristics, it should not exceed 270°C.

Mold temperature: 30~40°C for non-reinforced materials, 80~90°C for thin-walled or large components, 90~100°C for reinforced materials. Increasing temperature increases crystallinity of material. Precise mold temperature control is very important for PA12.

Injection pressure: up to 1000 bar (low holding pressure and high melting point recommended).

Injection speed: high speed (better for materials with glass additives).

Guide and gate: For materials without additives, due to low viscosity of material, diameter of gate should be about 30 mm. Reinforced materials require a large flow path diameter of 5~8mm. The shape of runner should be round. The injection port should be as short as possible. Various gate shapes can be used. Do not use small flaps on large plastic parts to avoid excessive pressure or excessive shrinkage of plastic parts. The thickness of gate is preferably equal to thickness of plastic part. If immersion valves are used, a minimum diameter of 0.8 mm is recommended. Hot runner molds are effective but require precise temperature control to prevent material from leaking or freezing at nozzle. When using a hot runner, size of runner must be smaller than cold runner.

Chemical and physical properties:

PA12 is a linear semi-crystalline thermoplastic material made from butadiene. Its properties are similar to PA11, but crystal structure is different. PA12 is a good electrical insulator and, like other polyamides, does not affect insulation performance due to moisture. It has good impact resistance and chemical stability. PA12 has many improved grades in terms of plasticizing and hardening properties. Compared to PA6 and PA66, these materials have a lower melting point and density, as well as a very high degree of moisture recovery. PA12 is not resistant to strong oxidizing acids. The viscosity of PA12 is mainly affected by humidity, temperature and storage time. It flows very well. The shrinkage rate is from 0.5% to 2%, which mainly depends on type of material, wall thickness and other process conditions.

4.PA66 polyamide 66 or nylon66

Typical application:

Compared with PA6, PA66 is more widely used in automotive industry, instrument housings and other products requiring impact resistance and high strength.

Injection molding process conditions:

Drying: If material is sealed before processing, drying is not required. However, if storage container is opened, it is recommended to dry it with hot air at 85°C. If humidity is above 0.2%, vacuum drying at 105°C for 12 hours is also required.

Melting point: 260~290℃. For products with glass additives, temperature is 275~280°C. Melting points above 300°C should be avoided.

Mold temperature: 80°C recommended. The temperature of mold will affect degree of crystallinity, which will affect physical properties of product. For thin-walled plastic parts, if mold temperature is lower than 40°C, crystallinity of plastic part will change over time. In order to maintain geometric stability of plastic part, annealing processing is required.

Injection pressure: typically 750-1250 bar, depending on product material and design.

Injection speed: high speed (slightly lower for reinforced materials).

Lobus and sprue: Because PA66's curing time is very short, sprue position is very important. The gate opening must not be less than 0.5*t (where t is thickness of plastic part). When using a hot runner, gate size should be smaller than when using a conventional groove, as hot runner can help prevent premature solidification of material. If a submersible valve is used, minimum valve diameter must be 0.75 mm.

Chemical and physical properties:

PA66 has a higher melting point than polyamide materials. It is a semi-crystalline crystalline material. PA66 can also maintain high strength and stiffness at higher temperatures. PA66 is still hygroscopic after molding, and its degree mainly depends on composition of material, wall thickness, and environmental conditions. The effect of hygroscopicity on geometrical stability must be taken into account when developing a product. Various modifiers are often added to improve mechanical properties of PA66. Glass is most common additive, and sometimes synthetic rubber such as EPDM and SBR is added to improve impact resistance. PA66 is less viscous so it flows well (but not as well as PA6). This property can be used to process very fine details. Its viscosity is sensitive to temperature changes. The shrinkage of PA66 is 1% to 2%, addition of glass fiber additives can reduce shrinkage to 0.2-1%. The difference in shrinkage in flow direction and direction perpendicular to flow direction is greater. PA66 is resistant to many solvents but is less resistant toacids and some other chlorinating agents.

5.PBT polybutylene terephthalate

Typical application:

Household appliances (food grade blades, vacuum cleaner components, electric fans, hair dryer housings, coffee utensils, etc.), electrical components (switches, motor housings, fuse boxes, computer keyboard keys, etc.), automotive industry (heat-dissipating glass, body panels, wheel covers, window and door elements, etc.).

Injection molding process conditions:

Drying: This material hydrolyzes easily at high temperatures, so drying before processing is very important. Recommended air drying conditions: 120°C for 6-8 hours or 150°C for 2-4 hours. Humidity should be less than 0.03%. When drying with a desiccant dryer, recommended conditions are: 150°C for 2.5 hours.

Melting point: 225~275℃, recommended temperature: 250℃.

Mold temperature: 40~60℃ for non-reinforced materials. The mold cooling channel must be well designed to reduce bending of plastic part. Heat loss must be rapid and uniform. It is recommended that diameter of mold cooling channel be 12mm.

Injection pressure: medium (up to 1500 bar).

Injection speed: The highest possible injection speed should be used (because PBT hardens quickly).

Guide and sprue: It is recommended to use a round guide to increase pressure transfer (empirical formula: guide diameter = plastic part thickness + 1.5 mm). Various types of gates can be used. Hot runners can also be used, but care must be taken to prevent leakage and material degradation. The gate diameter should be within 0.8~1.0*t, where t is thickness of plastic part. In case of immersion gates, a minimum diameter of 0.75 mm is recommended.

Chemical and physical properties:

PBT is one of strongest engineering thermoplastic materials. It is a semi-crystalline material with very good chemical stability, mechanical strength, electrical insulating properties and thermal stability. These materials have good stability over a wide range of environmental conditions. PBT has very weak hygroscopic properties. The tensile strength of non-reinforced PBT is 50 MPa, while with glass additives it is 170 MPa. Too much glass additive will make material brittle. PBT; crystallization occurs very quickly, which causes bending deformation due to uneven cooling. For materials with glass additives, shrinkage in direction of process can be reduced, but shrinkage in direction perpendicular to process is basically same as for conventional materials. As a rule, shrinkage ratio of materials is from 1.5% to 2.8%. material with 30% glass additive shrinks from 0.3% to 1.6%. Melting point (225°C) and high temperature deformation temperature are lower than PET materials. Vicat softening point is about 170°C. The glass transition temperature (glass transition temperature) is between 22°C and 43°C. Due to high crystallization rate of PBT, its viscosity is very low, and cycle time for processing plastic parts is usually short.

6. Polycarbonate PC

Typical application:

Electrical and commercial equipment (computer components, connectors, etc.), household appliances (food processors, refrigerator drawers, etc.), vehicles(car front and rear lights, dashboards, etc.) d.).

Injection molding process conditions:

Drying: Polycarbonate material is hygroscopic, so drying before processing is very important. Recommended drying conditions: 100°C to 200°C for 3-4 hours. Humidity before processing should be less than 0.02%.

Melting point: 260~340℃.

Mold temperature: 70~120℃.

Injection pressure: Use as high an injection pressure as possible.

Injection speed: use a slow injection speed for small sprues and a high injection speed for other types of sprues.

Chemical and physical properties:

PC is an amorphous construction material with particularly good impact strength, thermal stability, gloss, antibacterial properties, flame retardant properties and anti-pollution properties. Notched Izod impact strength of polycarbonate is very high, and shrinkage rate is very low, usually 0.1%~0.2%. PC has good mechanical properties but poor flow properties, so injection molding process of this material is more difficult. When choosing a quality polycarbonate material, they proceed from final expectations of product. If plastic part needs high impact resistance, please use PC material with low flow rate; on contrary, you can use high flow rate PC material, which can optimize injection molding process.

8. Polycarbonate PC/ABS and Acrylonitrile Butadiene Styrene Copolymers and Blends

Typical application:

Cases for computers and household appliances, electrical equipment, garden and lawn machines, auto parts (dashboards, interior trim, wheel covers).

Injection molding process conditions:

Drying: Drying required before processing. Humidity should be less than 0.04%, recommended drying conditions: 90~110℃ for 2~4 hours.

Melting point: 230~300℃.

Mold temperature: 50~100℃.

Injection pressure: depends on plastic part.

Injection speed: as high as possible.

Chemical and physical properties:

PC/ABS has all characteristics of PC and ABS. For example, ease of processing of ABS and excellent mechanical properties and thermal stability of PC. The ratio of these two factors will affect thermal stability of PC/ABS material. The PC/ABS hybrid material also exhibits excellent flow characteristics.

9. Blend of PC/PBT polycarbonate and polybutylene terephthalate

Typical application:

Gearboxes, automotive bumpers and products requiring chemical and corrosion resistance, heat resistance, impact resistance and geometric stability.

Injection molding process conditions:

Drying: It is recommended to dry at 110~135℃ for about 4 hours.

Melting point: 235~300℃.

Mold temperature: 37~93℃.

Chemical and physical properties:

PC/PBT has complex characteristics of both PC and PBT, such as high strength and geometric stability of PC, as well as chemical stability, thermal stability, and lubricity of PBT.

9.PE-HD high density polyethylene

Typical application:

Refrigerator containers, storage containers, household kitchen utensils, sealed lids, etc.

Injection molding process conditions:

Drying: If stored properly, drying is not required.

Melting point: 220~260℃. For materials with larger molecules, recommended melting temperature range is 200 to 250 °C.

Mold temperature: 50~95℃. Plastic parts with a wall thickness of less than 6mm should use a higher mold temperature, and plastic parts with a wall thickness of more than 6mm should use a lower mold temperature. The cooling temperature of plastic parts should be same to reduce shrinkage differences. For optimal cycle times, diameter of cooling channel should be at least 8 mm and within 1.3d of mold surface (where "d" is diameter of cooling channel).

Injection pressure: 700~1050 bar.

Injection speed: A high injection speed is recommended.

Guide and gate. The diameter of guide is between 4mm and 7.5mm, and length of guide should be as short as possible. Different types of sprues can be used, gate length should not exceed 0.75 mm. Particularly suitable for use with hot runner molds.

Chemical and physical properties:

The high crystallinity of PE-HD ensures its high density, tensile strength, high deformation temperature, toughness and chemical stability. PE-HD is more resistant to penetration than PE-LD. PE-HD has a lower impact strength. The properties of PH-HD are mainly controlled by density and molecular weight.ss distribution. The molecular weight distribution of PE-HD suitable for injection molding is very narrow. For density 0.91~0.925g/cm3 we call it first type PE-HD, for density 0.926~0.94g/cm3 we call it second type PE-HD, for density 0.94~0.965g/cm3, so called PE-HD of third type. The flow characteristics of this material are very good with an MFR of 0.1 to 28. The higher molecular weight, worse PN-LD flow, but better toughness. PE-LD is a semi-crystalline material with a high degree of shrinkage after molding, from 1.5% to 4%. PE-HD is susceptible to environmental stress cracking. Cracking can be reduced by using materials with very low flow characteristics to reduce internal stresses. PE-HD readily dissolves in hydrocarbon solvents at temperatures above 60°C, but its resistance to dissolution is higher than that of PE-LD.

10.PE-LD low density polyethylene

Typical application:

Bowls, cabinets, pipe connectors

Injection molding process conditions:

Drying: not usually needed

Melting point: 180~280℃

Mold temperature: 20~40℃. In order to achieve uniform cooling and economical heat dissipation, it is recommended that diameter of cooling channel be at least 8mm, and distance from cooling channel to surface of mold should not exceed 1.5 times diameter of cooling channel .

Injection pressure: up to 1500 bar.

Withstand pressure: up to 750 bar.

Injection speed: A high injection speed is recommended.

Guides and gates. Various types of rails and gates are available. PE-LD is especially suitable for hot runner molds.

Chemical and physical properties:

The density of commercial PE-LD materials is 0.91~0.94g/cm3. PE-LD is permeable to gases and water vapor. The high coefficient of thermal expansion of PE-LD is not suitable for processing durable products. If density of PE-LD is from 0.91 to 0.925 g/cm3, then its shrinkage is from 2% to 5%, if density is from 0.926 to 0.94 g/cm3, then its shrinkage rate is from 1.5% to 4%. %between. The current actual shrinkage rate also depends on parameters of injection molding process. PE-LD is resistant to many solvents at room temperature, but aromatic and chlorinated hydrocarbon solvents can cause it to swell. Like PE-HD, PE-LD is susceptible to environmental stress cracking.

11.PEI polyester

Typical application:

Automotive industry (engine accessories such as temperature sensors, fuel and air supply systems, etc.), electrical and electronic equipment (electrical connectors, printed circuit boards, chip packages, explosion-proof boxes, etc.), packageproducts, aircraft interior equipment, pharmaceutical industry (surgical instruments, instrument cases, non-implantable instruments).

Injection molding process conditions:

Drying. Handling: PEI is hygroscopic and may degrade material. The required humidity value should be less than 0.02%. Recommended drying conditions: 150°C, 4 hours drying.

Melting point: ordinary material 340~400℃, reinforced material 340~415℃.

Mold temperature: 107~175℃, recommended mold temperature 140℃.

Injection pressure: 700~1500 bar.

Injection speed: use highest possible injection speed.

Chemical and physical properties:

PEI has strong high temperature resistance, even if it is non-reinforced PEI, it still has good toughness and toughness. Therefore, excellent thermal stability of PEI can be used to make high temperature heat resistant devices. PEI also has good flame retardant, chemical resistance and electrical insulating properties. The glass transition temperature is very high, reaching 215°C. PEI also has very low shrinkage and good mechanical properties in same direction.

12.PET polyethylene terephthalate

Typical application:

Automotive (structural devices such as mirror boxes, electrical components such as headlight reflectors, etc.), electrical components (engine housings, electrical connectors, relays, switches, microwave oven internals, etc.) ). Industrial applications (pump housings, hand tools, etc.).

Injection molding process conditions:

Drying: drying before processing Necessary because PET is very hygroscopic. Recommended drying conditions: 120~165°C, 4 hours drying. The required humidity should be less than 0.02%.

Melting point: unfilled type: 265~280℃, glass filled type: 275~290℃.

Mold temperature: 80~120℃.

Injection pressure: 300~1300 bar.

Injection speed: Higher injection speeds can be used without causing embrittlement.

Rolls and gates: All common types of gates can be used. The size of gate should be 50~100% of thickness of plastic part.

Chemical and physical properties:

The glass transition temperature of PET is about 165°C, and crystallization temperature range of material is 120~220°C. PET has strong hygroscopicity at high temperature. For glass fiber reinforced PET materials, bending deformation also occurs very easily at high temperatures. The degree of crystallinity of material can be increased by adding a crystallization enhancer. Transparent products treated with PET have gloss and heat distortion temperature.and I. Special additives such as mica can be added to PET to minimize flexural deformation. Transparent products can also be produced using unfilled PET materials if lower mold temperatures are used.

13.PETG modified with ethylene glycol - polyethylene terephthalate

Typical application:

Medical equipment (tubes, reagent bottles, etc.), toys, monitors, light caps, protective masks, refrigerator fresh storage trays, etc.

Injection molding process conditions:

Drying: Drying required before processing. Humidity should be below 0.04%. Recommended drying conditions: 65°C for 4 hours, drying temperature should not exceed 66°C.

Melting point: 220~290℃.

Mold temperature: 10~30°C, recommended 15°C.

Injection pressure: 300~1300 bar.

Injection speed: Higher injection speeds can be used without causing embrittlement.

Chemical and physical properties:

PETG is a transparent, non-crystalline material. Glass transition temperature 88°C. The allowable process range of PETG injection molding is wider than that of PET, and it has comprehensive characteristics of transparency, high strength and high intentionality.

14.PMMA polymethylmethacrylate

Typical application:

Automotive industry (signal lighting equipment, dashboard, etc.), pharmaceutical industry (blood storage containers, etc.), industrial applications (video disc, diffuser), FMCG (beverage glasses, stationery goods, etc.) .

Injection molding process conditions:

Drying: PMMA is hygroscopic, so drying is necessary before processing. Recommended drying conditions: 90°C for 2-4 hours.

Melting point: 240~270℃.

Mold temperature: 35~70℃.

Injection speed: medium

Chemical and physical properties:

PMMA has excellent optical properties and weather resistance. White light penetration reaches 92%. PMMA products have very low birefringence and are particularly suitable for videodisc applications. PMMA has creep properties at room temperature. As load increases and time increases, this can lead to stress cracking. PMMA has good impact resistance.

15.POM Polyoxymethylene

Typical application:

POM has a very low coefficient of friction and good geometrical stability, especially suitable for gears and bearings. Because it also has high temperature resistance properties,it is also used in plumbing components (pipe valves, pump housings), lawn equipment, etc.

Injection molding process conditions:

Drying: Drying is not normally required if material is stored in a dry environment.

Melting point: 190~230℃ for homopolymer materials, 190~210℃ for copolymer materials.

Mold temperature: 80~105℃. To reduce shrinkage rate after molding, a higher mold temperature can be selected.

Injection pressure: 700~1200 bar

Injection speed: medium or high injection speed.

Guides and gates: any type of gate can be used. If tunnel gates are used, it is better to use a shorter type. For homopolymer materials, hot nozzle runners are recommended. For copolymer materials, both internal and external hot runners can be used.

Chemical and physical properties:

POM is a strong and elastic material with good creep resistance, dimensional stability and impact resistance even at low temperatures. POM has both homopolymer and copolymer materials. Homopolymer materials have good tensile strength and fatigue resistance, but are not easy to process. Copolymer materials have good thermal stability, chemical stability and ease of processing. Both homopolymer and copolymer materials are crystalline materials and do not absorb moisture well. The high degree of crystallinity of POM results in a relatively high shrinkage rate, which can be as high as 2% to 3.5%. There are different degrees of shrinkage for different reinforced materials.

Polypropylene 16.PP

Typical application:

Automotive industry (mainly using polypropylene containing metal additives: fenders, vent pipes, fans, etc.), household appliances (dishwasher door gasket, dryer vent pipe, washing machine body and cover, refrigerator door gasket etc.), consumer goods (lawn and garden equipment such as

Lawn mowers, sprinklers, etc.).

Injection molding process conditions:

Drying: If stored properly, drying is not required.

Melting point: 220~275°C, do not exceed 275°C.

Mold temperature: 40~80°C, recommended 50°C. The degree of crystallization is mainly determined by mold temperature.

Injection pressure: up to 1800 bar.

Injection speed: In general, internal pressure can be minimized with high speed injection molding. If defects appear on surface of part, low speed injection molding at higher temperatures should be used.

Guides and sprues. Standard guide diameterinfluencing for cold gates is from 4 to 7 mm. It is recommended to use a sprue and runner with a round body. All types of gates can be used. Typical gate diameters are between 1 and 1.5 mm, but gates as small as 0.7 mm can also be used. For end gates, minimum depth of gate must be half thickness of wall, minimum width of gate must be at least twice thickness of wall. PP material can make full use of hot runner.

Chemical and physical properties:

PP is a semi-crystalline material. It is harder and has a higher melting point than polyethylene. Since polypropylene homopolymer is very brittle at temperatures above 0°C, many commercial polypropylene materials are random copolymers with 1 to 4% ethylene content or clamp copolymers with higher ethylene content. Copolymer polypropylene materials have a low heat distortion temperature (100°C), low transparency, low gloss and low stiffness, but have higher impact strength. The strength of PP increases with increasing ethylene content. The Vicat softening temperature of polypropylene is 150°C. Due to its high degree of crystallinity, this material has very good surface hardness and scratch resistance. Polypropylene has no problems with environmental stress cracking. Typically, polypropylene is modified by adding fiberglass, metal additives, or thermoplastic rubber. The MFR consumption of PP ranges from 1 to 40. Low MFR polypropylene materials have better impact resistance but lower tensile strength. For phase C with MFR materials, strength of copolymer type is higher than that of homopolymer type. Due to crystallization, degree of shrinkage of polypropylene is quite high, typically 1.8–2.5%. And shrinkage direction uniformity is much better than PE-HD and other materials. The addition of 30% glass additive can reduce shrinkage to 0.7%. Both homopolymer and copolymer polypropylene materials have excellent resistance to moisture absorption, acid and alkali corrosion, and dissolution resistance. However, it does not have resistance to aromatic hydrocarbon (such as benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, etc. PP still does not have high temperature oxidation resistance like PE.

17. PPE Polypropylene

Typical application:

Household items (dishwashers, washing machines, etc.), electrical equipment such as controller cases, fiber optic connectors, etc.

Injection molding process conditions:

Drying: It is recommended to dry at 100℃ for 2-4 hours before processing.

Melting point: 240~320℃.

Mold temperature: 60~105℃.

Injection pressure: 600~1500 bar.

Leggings and gates: all types of gates can be used. Particularly suitable for use with manual gates and fan gates.

Chemical and physical properties:

Commonly commercially available PPE or PPO materials are usually blended with other thermoplastic materials such as polystyrene, polyamide, etc. These hybrid materials are usually still referred to as PPE or PPO. Blended PPE or PPO have much better processing characteristics than pure material. Properties vary depending on ratio of mixtures such as PPO and PS. Hybrid materials mixed with PA 66 have higher chemical stability at high temperatures. This material is slightly hygroscopic, and products made from it have excellent geometric stability. The material blended with polystyrene is non-crystalline while material blended with polyamide is crystalline. The addition of glass fiber additives can reduce shrinkage to 0.2%. This material also has excellent electrical insulating properties and a very low coefficient of thermal expansion. Its viscosity depends on mixture ratio in material, and increasing ratio of PFO will increase viscosity.

Polystyrene 18.PS

Typical application:

Product packaging, household goods (dishes, trays, etc.), electrical engineering (transparent containers, light source diffusers, insulating films, etc.).

Injection molding process conditions:

Drying: Drying is not normally required, unless stored properly. If drying is required, recommended drying conditions: 80°C for 2-3 hours.

Melting point: 180~280℃. For fire resistant materials, upper limit is 250°C.

Mold temperature: 40~50℃.

Injection pressure: 200~600 bar.

Injection speed: A high injection speed is recommended.

Rolls and gates: All common types of gates can be used.

Chemical and physical properties:

Most commercially available polystyrenes are a transparent, non-crystalline material. PS has very good geometrical stability, thermal stability, optical transmission properties, electrical insulating properties and very low hygroscopic tendency. It is resistant to water and dilute inorganic acids, but can be corroded by strong oxidizing acids such as concentrated sulfuric acid, and can also swell and warp in some organic solvents.

Typical shrinkage is 0.4 to 0.7%.

19.PVC (polyvinyl chloride)

Typical application:

Water pipes, household pipes, house wall panels, commercial vehicle enclosures, electronic packagingproducts, medical equipment, food packaging, etc.

Injection molding process conditions:

Drying: Normally, drying is not required.

Melting point: 185~205℃

Mold temperature: 20~50℃

Injection pressure: up to 1500 bar

Withstand pressure: up to 1000 bar

Injection speed: In order to avoid degradation of material, a significant injection speed is usually used.

Leggings and gates: All regular gates can be used. Pin sprues or dip sprues are best for small parts, fan sprues are best for thicker parts. The minimum diameter of a point or immersion valve must be 1 mm, thickness of a fan valve must be at least 1 mm.

Chemical and physical properties:

Rigid PVC is one of most widely used plastic materials. PVC material is a non-crystalline material. PVC materials are often added with stabilizers, lubricants, auxiliary processing agents, dyes, impact agents and other additives in actual use. PVC material is non-combustible, high strength, resistant to climatic changes and excellent geometric stability. PVC is highly resistant to oxidizing agents, reducing agents and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid, and is not suitable for contact with aromatic hydrocarbons and chlorinated hydrocarbons. The melting temperature of PVC is a very important process parameter in processing, wrong choice of which will lead to problem of material decomposition. The flow characteristics of PVC are rather poor, and its processing range is very narrow. In particular, high molecular weight PVC materials are more difficult to process (lubricants usually need to be added to such materials to improve flow characteristics), so low molecular weight PVC materials are usually used. The shrinkage rate of PVC is quite low, typically 0.2–0.6%.

Copolymer of styrene and acrylonitrile 20.SA

Typical application:

Electrical (sockets, enclosures, etc.), FMCG (kitchen appliances, refrigerators, TV stands, cassette boxes, etc.), automotive (headlight boxes, reflective covers, dashboards, and etc.), household products (dishes, kitchen knives, etc.), cosmetic packaging, etc.

Injection molding process conditions:

Dry Processing: SA has some hygroscopic properties when stored improperly. Recommended drying conditions: 80°C, 2~4 hours.

Melting point: 200~270℃. When processing thick-walled products, melting temperatures belowlower limit.

Mold temperature: 40~80℃. For reinforced materials, mold temperature should not exceed 60°C. The cooling system must be well designed because temperature of mold directly affects appearance, shrinkage and bending of part.

Injection pressure: 350~1300 bar.

Injection speed: A high injection speed is recommended.

Leggings and gates: All regular gates can be used. Gates must be properly sized to avoid streaks, burnt spots and voids.

Chemical and physical properties:

SA is a hard transparent material. The styrene component makes SC hard, transparent and easy to process, acrylonitrile component makes SC chemically and thermally stable. SA has high load-bearing capacity, resistance to chemical reactions, thermal stability and dimensional stability. The addition of fiberglass additives to SA can increase strength and resistance to thermal deformation, as well as reduce coefficient of thermal expansion. The Vicat softening point SA is about 110°C. The deflection temperature under load is about 100°C. SA shrinkage rate is about 0.3~0.7%.